The Department of Education should have acted long ago, after the school’s teachers-union chapter passed a rare vote of no confidence in Ben Sherman, the principal. Or earlier, when faculty informally sent word of trouble up the chain via the United Federation of Teachers.

Heck, responsible educrats would’ve been asking questions after last year’s “school climate survey” revealed that only 55 percent of Forest Hills teachers agreed that order and discipline are maintained at the school, well below the citywide average of 77 percent — at what’s long been an excellent school.

Yet teachers had to come to The Post to get action. (Should we send UFT chief Mike Mulgrew an invoice for having the Post do his job?)

Now the local city councilwoman, Karen Koslowitz, is demanding a full DOE investigation. Yet schools Chancellor Richard Carranza says only, “We are all working collectively to address issues at the school.” His minions report that the Queens superintendent for high schools is “investigating the complaints and strengthening oversight of the entire building and campus.”

But no sign of any probe into why DOE wasn’t on top of this mess before it hit our front page.

Of course, we’ve lost track of the times Team de Blasio has rushed to address a crisis only after our pages made it a public scandal. Who would’ve thought that the best way to get help in de Blasio’s New York would be to appeal to The Post?